In recent years, high integration and an increase in size of a semiconductor element have been advanced, and a package substrate is required to be further thinner and smaller. Accordingly, a surface protective layer of the semiconductor element, an interlayer insulating film, or an interlayer insulating film of the package substrate including a rewiring layer is required to be formed by a material having excellent electrical properties, heat resistance, mechanical properties and the like in combination.
A polyimide resin (hereinafter, referred to as “PI”) or polybenzoxazole (hereinafter, referred to as “PBO”) is a representative of the material which is able to satisfy the above required properties, and for example, use of a photosensitive PI or a photosensitive PBO, in which photosensitive properties have been imparted to PI or PBO, has been reviewed. If these photosensitive resins are used, there is an advantage in that a pattern formation step is simplified and a complicated manufacture step can be reduced. Furthermore, since the photosensitive resins have high heat resistance or insulation resistance compared to a conventional vinyl-based photosensitive resin which can be developed in alkali due to the introduction of a carboxyl group, the photosensitive resins are effective as the interlayer insulating film (for example, refer to PTLs 1 and 2).
On the other hand, the photosensitive PI or the photosensitive PBO has a problem in that the resins need to be baked at high temperature (350° C. to 400° C.); exposure stability is not satisfactory; film shrinkage of the formed resin film is great; and solubility in a solvent is low.
In contrast, an interlayer insulating film using a photosensitive alkali resin with high heat resistance and excellent handleability has been suggested (PTL 3). However, various lithography properties of this interlayer insulating film using this photosensitive alkali resin still need to be improved.